1. Field of the Invention
The present invention relates to a plasma display device using a plasma display panel.
2. Description of the Related Background Art
A plasma display device includes a plasma display panel which has a plurality of display cells corresponding to pixels, respectively. The plasma display device renders a grayscale display by constituting one field (or one frame) of an image signal by means of a plurality of subfields each of which includes an address period and a sustain period as a period of time. In the address period, either one of a lit mode state where wall electric charge exists and an unlit mode state where wall electric charge does not exist is set by causing each of the display cells of the plasma display panel to be selectively discharged on the basis of an input image signal. Further, in the sustain period, only the display cells that have been set in the lit mode state are allowed to retain the light-emitting state in which a sustain discharge is repetitively performed by the number of times corresponding to the weight of each of the subfields.
Further, a reset period for initializing the states of all the display cells is provided immediately before the address period of each of the subfields. In the reset period, first a write reset discharge for forming wall electric charge in all the display cells is induced and, by successively inducing an erase reset discharge for erasing the wall electric charge formed in all the display cells, all the display cells are initialized in an erase mode state. However, since light emission accompanying the reset discharge is not involved in the display image according to the input image signal and is induced all together in all the display cells, the contrast of the display image and, in particular, the dark contrast while displaying an image representing a dark scene drops. Therefore, a drive method for suppressing a drop in contrast by setting the number of reset discharges in the display period of one field (or one frame) as only one has been proposed (Japanese Patent Application Kokai No. H11-65517, for example).
When the number of reset discharges is set at only one, discharge delay occurs in the various discharges in subsequent address period and sustain period. Thus, it is necessary to widen the pulse width of each drive pulse that is applied to the plasma display panel to induce the various discharges. However, since the address period and sustain period are respectively made longer in accordance with the widening portion of the pulse width, there has been the problem that it is difficult to increase the number of display grayscales by increasing the number of subfields.